An inorganic GaN light emitting diode (LED) has characteristics of high efficiency, high brightness, and long life. However, GaN in the inorganic GaN LED is grown by using a sapphire substrate or a silicon substrate. Accordingly, there are limitations in producing various types of products and it is more particularly difficult to realize flexible or stretchable products.
Recently, John Rogers group has introduced a method of transferring an AlInGaP LED onto a flexible substrate. In this method, an AlGaAs layer is used as a sacrificing layer, and the sacrificing layer is etched in selective wet etching. Also, the method discloses a process of transferring a product onto polydimethylsiloxane (PDMS) on which electrodes are formed in advance.
However, this method has limitations as the followings.
1) AlGaN and GaN have low wet-etching selectivity. Accordingly, It is very difficult to apply a method, which uses a sacrificing layer, to a process of manufacturing a GaN based LED.
2) Since a separated product itself is not a device, there is inconveniency to transfer the separated product onto another substrate on which electrodes are formed and put it into contact with the electrodes.
3) Since the electrodes have simply mechanical contacts, problems may occur in ohmic contacts of the electrodes.
4) The product obtained by etching the sacrificing layer has a mesa structure. Accordingly, high-precision alignment is necessary in order to prevent light emitting efficiency from being reduced due to surface recombination.
Furthermore, a method of manufacturing a transferable GaN LED by using weak inter-layer coupling of graphite chunk (HOPG) or boron nitride (BN) has been introduced. However, this method is limited to a very small sized LED and difficult to apply to a device because transfer is performed only in a film type.